Idle hunting and bucking on acceleration mystery

What is your question?

In any gear, at any RPMs, at any engine temperature, if I apply the accelerator normally, the car bucks violently. I can overcome it somewhat by increasing the RPMs to 4000-5000 and slowly engaging the clutch but it's still rough. At idle it hunts at low RPMs between 500-800 at about a 1 second interval, never settling. Vacuum on the manifold at idle goes between 15-18 rhythmically. MAF sensor, clutch, and spark plugs have been replaced recently but did not change the symptoms. Cleaned the throttle body with SeaFoam spray. I ran the throttle idle calibration and it helped the idle a little but driving is still not any better. Nothing seems to change the way it runs. Any ideas?